Massive MIMO systems scale up conventional MIMO systems by possibly orders of magnitude, i.e., hundreds of antennas at a Base-Station (BS) to simultaneously serve tens of User Equipments (UEs) in the same time-frequency resource. Such a system may provide tremendous advantages in spectral efficiency. With the capabilities of aggressive spatial multiplexing and great array gains, a massive MIMO system may achieve capacity increase and energy efficiency improvement simultaneously. In addition, it can be built with inexpensive and low-power components. It also has the potential to significantly reduce the latency of the air interface, simplify the media access layer, as well as increase the robustness to both unintentional artificial interference and intended jamming. In general, massive MIMO systems are considered in Time Division Duplexing (TDD) mode, taking advantages of the channel reciprocity between the uplink and downlink, although Frequency Division Duplexing (FDD) is arguably possible. Moreover, Orthogonal Frequency Division Multiplexing (OFDM) is still the best technology to multiplex UEs in the whole bandwidth like the 4th Generation (4G) communication systems as it is very suitable for the MIMO system. Therefore, massive MIMO combining with OFDM would increase spectrum efficiency more than ten times of the conventional systems with a relatively simple implementation.
When massive MIMO is employed in the TDD communication systems, the downlink channel between the BS and UEs are estimated through the uplink pilot or sounding reference signal (SRS) transmitted by each UE by making use of the channel reciprocity of TDD systems. In addition to the CSI, the SINRs of the uplink and downlink of each UE also have to be estimated so that the BS can predict the achievable transmission rate and select the proper modulation and code scheme (MCS) for each UE. Even though, the estimated SINR cannot reflect the channel quality of each UE in a MU-MIMO user group accurately because of the unavoidable CSI estimation error. Hence, the CSI error level of each UE is also required so that the SINR decrease caused by CSI error can be approximated and incorporated when selecting the MCS for a UE. Due to the above reasons, this invention provides methods to estimate the SINR and the CSI error level of each UE based on the estimated uplink channel coefficients of each UE.
This invention presents embodiments that provide the signal transmission, detection methods and the relative processes for the downlink and uplink transmission in massive MIMO systems.